Retention of a backward classically conditioned reflex response in spinal cat.

Retention of a backward classically conditioned reflex response was investigated in the spinal cat preparation. Facilitation of the flexion reflex was induced by the pairing of superficial peroneal nerve stimulation (30 Hz, 0.5 s), the US (unconditioned stimulus), with saphenous nerve stimulation (10 Hz, 1.5 s), the CS (conditioned stimulus). Both the US and CS were supramaximal for activation of A delta cutaneous afferent fibers. Experimental animals received 30 paired trials (US preceded CS by 0.25 s) with an intertrial interval (ITI) of three min. Control animals received the same stimuli but in an explicitly unpaired manner. Following acquisition, all animals received 30 additional CS-alone trials at five min intervals. This paradigm, which incorporated ITIs longer than those which had been used previously in backward conditioning studies, induced a long-lasting potentiation of the flexion reflex which appeared to be specific to spinal reflex pathways activated by A alpha cutaneous fibers. The relevancy of these results to a more specific understanding of backward and forward classical conditioning in the spinal cat is discussed.